306 The Principles of Vegetable- Oar dening 



has shown (Proc. Soc. Prom. Agr. Sci., 1891, p. 11; Bull. 42, 

 Purdue Univ.) that the unit in such tests should not be the num- 

 ber of eyes to the piece, but the size of the piece. The piece 



Fig. 83. A potato sorter. 



contains food. The more food the stronger the initial growth of 

 the plant: and the stronger the initial growth, the better the crop, 

 other things being equal. But if the piece is too large it contains 

 so many eyes that there will be too many stalks to appropriate the 

 food and to struggle with each other. The pieces on the tip or 

 "seed end" may contain several eyes, but those from the other 

 parts of the tuber usually should contain only one or two eyes. 

 See Fig. 84. Seed should not be cut any considerable time in ad- 

 vance of planting unless it is rolled in plaster. 



The varieties of potatoes are numerous and poorly defined, 

 and it is not worth the while to enumerate any of them here. In 

 the year 1889 the seed merchants of the United 

 States are known to have offered at least 889 va- 

 rieties (Annals Hort.). Because of variation and 

 inattention to selection, varieties of potatoes soon 

 run out (see "Survival of the Unlike"). 



One of the most interesting chapters in the 

 A good cutting or history of pestilential diseases of plants is afforded 

 seed-piece. virulent spread of potato blight. It caused 



the famine in Ireland in 1846. It overran this country. Periodi- 

 cally it is serious at the present day, although it cannot with- 

 stand Bordeaux mixture when the material is applied early and 



